So I don't see that this has been mentioned before... how do you guys feel about being able to remove aspects after placing them? I think this would reduce frustration a lot, since it could (1) allow you to remove an replace an aspect after you upgrade it, (2) allow you to remove an aspect and replace it with a different one that you just unlocked, (3) retry for the "better" version of an aspect without having to completely start over every time. Thoughts?

It would make the game too easy... :)
And it will remove a lot of meaning from the challenge achievements :)
From basic chemistry, nearly all reactions are irreversible, so I think creating a resourse anew to try again is kind of more "natural" way :)
Same goes to plants, when you alter them there's no reverting back. And somewhat similar logic is with animals

I'd rather have the option of swapping ambassadors but every time I think about it, I instantly think it would also be too easy, and it will remove the reading up and prior planning of an era with a notepad, so this thing is better remain unimplemented either :)